Modem computers are often connected via networks, so that they can communicate with each other and share information. The Internet is an example of one such network. Computers send information to each other on the network via packets, which are collections of related data. In some networks, source computers routinely broadcast packets to all computers attached to the network, even though the intended destination is only one computer, or perhaps a subset of the computers. In other networks, the source and destination computers are not directly connected to each other, so a packet might need to travel through multiple computers before reaching its final destination. In both of these types of networks, a computer can receive large numbers of packets for which it is not the intended destination.
Since it is inefficient for a networked computer to waste its time and energy examining large numbers of packets for which it is not the intended destination, a networked computer typically offloads this function to a network adapter, through which the computer (called the host computer) attaches to the network. It is thus the job of the network adapter to examine each received packet, determine its intended destination, and present the received packet to the adapter's host computer only if the packet is intended for it. Otherwise, the network adapter merely discards the packet or forwards it through the network.
In order to save electricity, the host computer typically enters a power-managed state when it is not receiving packets. During a power-managed state, the host computer uses less electricity by powering down or reducing electricity to selected computer components. When the network adapter detects a packet for which the host computer is the final destination, the adapter sends the host a wake-up signal, which causes the host to return to its operational working state, so that the host is capable of processing the received packet, and so that other hosts on the network can access its resources, such as web pages, files, printers, applications or services.
Unfortunately, unauthorized persons or programs (often called hackers) will probe the network to find hosts that are running applications or services that can be attacked. These hackers attempt to access the host computer by sending packets that contain the destination address of the host computer. Since the host network address matches the address in the packet, the network adapter sends the host a wake-up signal causing it to wake up, even if there are no applications or services running that can respond to the received packet. This wastes the host's time and energy and makes the host vulnerable to attack. Thus, there is a need for a solution that will protect a computer in a network from attack by unauthorized users and allow it to stay in the power-managed state until it receives a relevant packet.